5. Fluid Dynamics + Peripheral Circulation

Question 1

Define velocity

Answer 1

The rate of movement of fluid particles along a tube

Question 2

What is the relationship between velocity and radius for a constant flow?

Answer 2

Velocity is inversely proportional to the radius squared

The greater the cross sectional area the slower the velocity

Question 3

What is laminar flow?

Answer 3

Where the velocity is greatest in the middle of the vessel and there is a velocity gradient to the edge

Question 4

What can cause turbulent flow and what does it result in?

Answer 4

Velocity increasing to a point where the flow becomes turbulent
Laminar flow breaks down and resistance is increased greatly

Question 5

How can you detect turbulent flow?

Answer 5

Creates a noise called bruit

Question 6

For a constant pressure what is the relationship between velocity and viscosity?

Answer 6

Velocity is inversely proportional to viscosity

The thicker the blood is, the slower it travels

Question 7

For a constant pressure, what is the relationship between velocity and radius of tube?

Answer 7

As flow is determine by the velocity
Velocity is proportional to radius squared

The wider the tube the faster the blood will travel

Question 8

Why does increasing radius increase velocity at constant pressure?

Answer 8

The wider the tube the faster the middle layers will move as the velocity gradient is constant

Question 9

According to poiselles law, what is the relationship between difference in pressure at both ends of a tube and radius at a constant flow and viscosity?

Answer 9

Difference in pressure is inversely proportional to radius to the power of 4

Question 10

What is the relationship between resistance and viscosity?

Answer 10

Resistance increases as viscosity increases

Question 11

What is the relationship between resistance and radius?

Answer 11

Resistance decreases with radius to the power of 4

Question 12

Define flow

Answer 12

Volume of fluid that passes a given point per unit of time

Question 13

What variables are pressure equal to?

Answer 13

Pressure= flow x resistance

Similar to ohms law with electrical current

Question 14

What is the relationship between flow and radius for a given pressure?

Answer 14

Flow is proportional to radius to the power of 4

Question 15

What is the relative pressure size drop over the arteries?

Answer 15

Small

Question 16

What is the relative pressure drop size over arterioles?

Answer 16

Large

Question 17

What happens to flow in distensible vessels as pressure is increased and why?

Answer 17

As pressure increases flow increases because:
Increase in pressure causes vessel to stretch
This increases the cross sectional area of the vessel hence flow increases (to the 4th power of the change in radius)

Question 18

How do veins have capacitance?

Answer 18

A transient increase in pressure will cause more blood to flow into the vessel than out (and vice versa) allowing blood to be “stored” in veins

Question 19

Why does arterial pressure need to be high?

Answer 19

To drive the cardiac output through the total peripheral resistance

Question 20

Why do arteries have distensible walls?

Answer 20

So in systole they stretch (more blood flows in than out) hence pressure does not rise too much
As arteries recoil flow continues into arterioles

Question 21

What factors affect systolic pressure?

Answer 21

How hard the heart pumps
Total peripheral resistance
Stretchiness of arteries

Question 22

What factors affect diastolic pressure?

Answer 22

Systolic pressure

Total peripheral resistance

Question 23

What is pulse pressure? (Give a typical value)

Answer 23

Difference between systolic and diastolic pressures

Typically about 40mmHg

Question 24

How is average pressure calculated?

Answer 24

Diastolic pressure + 1/3 pulse pressure

Question 25

What properties make arterioles high resistance vessels?

Answer 25

Lumen is narrow

High smooth muscle cell content

Question 26

What are increases and decreases in vasomotor tone called?

Answer 26

Vasoconstriction

Vasodilatation

Question 27

Name 3 vasodilator metabolites

Answer 27

H+
K+
Adenosine

Question 28

How is blood flow matched to rate of metabolism?

Answer 28

Rate of metabolism leads to a proportional amount of metabolites to be produced
Blood flow is then balanced between the rate at which they are produced and how quickly they are washed away